The invention relates to packaging for metal-ceramic substrates having a tray-like packaging part formed from a sheet material. The invention is also directed to a packaging unit for a substrate stack or part stack.
Metal-ceramic substrates, in particular those in the form of circuit boards for electrical and electronic circuits or modules, as well as methods for the manufacture of such substrates are known. As a rule, such substrates consist of a ceramic insulating layer which is provided on both surfaces with a metallization. This latter is, for example, produced from a metal foil, for example of copper, or a copper alloy, which is flat bonded with the ceramic insulating layer using a suitable assembly method.
An example of the assembly method is the so-called “DCB method” (direct copper bond technology), for example, for bonding metal layers or sheets (for example copper sheets or foils) together and/or to ceramics or ceramic layers, using metal or copper sheets, or metal or copper foils, which have a layer or coating (“melt layer”) on the surfaces formed from a chemical compound formed from the metal and a reactive gas, preferably oxygen. In this method, described, for example, in U.S. Pat. No. 3,744,120 or in DE-PS 23 19 854, this layer or coating (“melt layer”) forms a eutectic with a melting point that is below the melting point of the metal (for example copper), so that by applying the foil to the ceramic and heating all of the layers, they can be bonded together by melting the metal or copper only in the zone of the melt layer or oxide layer.
Such a DCB method then, for example, has the following process steps:                oxidizing a copper foil in a manner so as to produce a uniform copper oxide layer;        applying the copper foil to the ceramic layer;        heating the assembly to a process temperature between about 1025° C. and 1083° C., for example to about 1071° C.;        cooling to room temperature.        
Similar to the DCB method cited above for direct bonding of copper onto copper or copper onto ceramic, other direct metal bonding methods or technologies are known by means of which, in an analogous manner, metal layers or sheets can quite generally be bonded together and/or bonded with ceramic or ceramic layers. The DCB method and the methods analogous thereto will hereinafter be termed DMB methods (direct metal bond method).
Further, the so-called active brazing method is known (DE 22 13 115; EP-A-153 168), e.g. for bonding metal layers or metal foils forming metallizations, especially copper layers or copper foils or aluminium layers or aluminium foils with a ceramic material. In that method which, for example, can also be specifically used for the manufacture of metal-ceramic substrates, a bond between a metal foil, for example, copper foil, and a ceramic substrate, for example an aluminium nitride ceramic, is produced at a temperature of between approximately 800-1000° C. using a brazing solder which, in addition to a main component such as copper, silver and/or gold, also contains an active metal. This active metal which is, for example, at least one element from the group Hf, Ti, Zr, Nb and Ce, produces a bond between the brazing solder and the ceramic by a chemical reaction, while the bond between the brazing solder and the metal is a metallic brazing solder bond.
It is an object of the invention to provide packaging which allows substrates, in particular and including metal-ceramic substrates, to be transported and stored safely.
The term “substrate” as used in the context of the invention primarily means board-like products, preferably rectangular or square board-like products, for example substrates for electrical and electronic applications, in particular in the form of circuit boards and special metal-ceramic substrates.
The term “substrate stack” as used in the context of the invention refers to a stack formed from substrates sitting closely against one another and/or mutually supporting each other, wherein the thickness of the stack in the stacking direction, i.e. in the direction perpendicular to the top surfaces of the substrates, is equal to or essentially equal to the distance between the lateral structures of the at least one substrate seat in the lower portion of the packaging.
The term “part stack” as used in the context of the invention means a stack formed from at least two, but preferably from more than two substrates mutually supporting each other, wherein the thickness of the stack in the stacking direction, or perpendicular to the top surfaces of the substrates, is less than the distance between the lateral structures of the at least one substrate seat in the lower portion of the packaging.
A “packaging unit” as used in the context of the invention means the packaging which is at least partly filled with metal-ceramic substrates, preferably the packaging which is at least partly filled with metal-ceramic substrates, sealed and placed in a sealed and evacuated wrapper. The packaging unit may also contain two or more than two packagings at least partly filled with metal-ceramic substrates in a sealed and evacuated wrapper.
The expression “essentially” or “about” as used in the context of the invention mean deviations from the respective exact value by ±10%, preferably by ±5% and/or deviations in the form of differences which are irrelevant to function.